Abstract
Entomopathogenic nematodes (EPNs) are among the frequently used and commercialized bio-pesticides. However, they are restricted in their infectivity, persistence, storage, and cost of production. One of the methods used to improve this is a continuous search for new isolates with significant behavioral and physiological characteristics. A novel EPN isolate, Heterorhabditis zealandica strain ETL, isolated from South Africa (GPS co-ordinates − 24.849721 and 28.336980) is described and studied against late-instar of Galleria mellonella (L.) and Tenebrio mollitor (L.) larvae. The morphological and molecular studies indicated this isolate as a Heterorhabditis strain. The comparison of sequences of the internal transcribed spacer (ITS) region, the 18S rRNA gene, and the D2-D3 region of the 28S rRNA gene with available sequences of other described species within the genus indicate the isolate as a new Heterorhabditis zealandica strain. The phylogenetic analysis of the sequence data places strain ETL, closest to H. zealandica strain Bartow (GU174009) in the Heterorhabditis group. This EPN was lethal to G. mellonella and T. mollitor; as infections occurred within 24–96 h. Fifty percent of the larvae population were killed within 24 h and 100% after 96 h.
Highlights
Entomopathogenic nematodes (EPNs) are highly pathogenic to numerous insect pests (Malan and Ferreira 2017)
Effective biocontrol agents of insects have been mainly isolated from the genera Steinernema and Heterorhabditis, which are mutually associated with bacteria of the genera Xenorhabdus and Photorhabdus, respectively (Malan and Ferreira 2017)
Of the 4 samples, only one sample displayed complete virulence against the larvae allowing subsequent Infective juvenile (IJ) production for further study. This represents a low recovery, this study highlights the need for more EPN surveys and studies in the northern parts of South Africa (SA)
Summary
Entomopathogenic nematodes (EPNs) are highly pathogenic to numerous insect pests (Malan and Ferreira 2017). Molecular characters are considered as the most suitable approach for species identification and systematics of nematodes, especially for taxonomic ambiguities, identification of members of a species complex, and the differentiation of morphologically similar species (Peat et al 2009). They have been widely used (Peat et al 2009; CamposHerrera 2015). Nuclear genes have been used extensively; each has numerous copies and evolves at different rates Their variable and conserved regions render it possible to differentiate taxonomic levels and delimitate the nematode taxa (Stock 2009). The aim of this study was to isolate and identify a native EPN species that can be suitable as a biocontrol agent by testing it against Galleria mellonella L. and Tenebrio mollitor L. larvae under laboratory conditions
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